The present invention generally relates to electronic components and more particularly, to a rotary operation type miniaturized electronic component, for example, a miniaturized variable resistor, a miniaturized switch, etc., for use in various electronic video and audio appliances and the like.
As a prior art of the present invention, a conventional interlocking type miniaturized variable resistor K will be described by way of example with reference to FIGS. 1 to 3, hereinbelow. The known interlocking type miniaturized variable resistor K generally includes a casing 1 of cylindrical shape, a first insulating substrate 2 formed with a central bore 22, a second insulating substrate 3 formed with a central bore 23, and a retainer 4 having a pair of legs 5 such that the first and second insulating substrates 2 and 3 are, respectively, secured to upper and lower ends of the casing 1 by the legs 5 of the retainer 4. Additionally, as shown in FIGS. 2 and 3, a first resistance element 6 of circular shape and a first conductor 8 of circular shape, which are provided coaxially with each other about an axis of the casing 1 such that the first resistance element 6 is disposed radially outwardly of the first conductor 8, are formed on a lower surface of the first insulating substrate 2 by printing, etc. Similarly, a second resistance element 7 of circular shape and a second conductor 9 of circular shape, which are provided coaxially with each other about the axis of the casing 1 such that the second resistance element 7 is disposed radially outwardly of the second conductor 9, are formed on an upper face of the second insulating substrate 3 in alignment with the first resistance element 6 and the first conductor 8 of the first insulating substrate 2, respectively by printing, etc. so as to confront the first resistance element 6 and the second conductor 8, respectively. Furthermore, a pair of terminals 10 and 12 and a terminal 14 are, respectively, attached to opposite ends of the first resistance element 6 and the first conductor 8 by caulking and are bent downwardly so as to be inserted into mounting holes of a printed circuit board 16, respectively such that the terminals 10, 12 and 14 are electrically connected to the printed circuit board 16. Likewise, a pair of terminals 11 and 13 and a terminal 15 are, respectively, attached to opposite ends of the second resistance element 7 and the second conductor 9 by caulking and are bent downwardly so as to be inserted into mounting holes of the printed circuit board 16, respectively such that the terminals 11, 13 and 15 are electrically connected to the printed circuit board 16. Moreover, a pair of mounting legs 17 for mounting the casing 1 on the printed circuit board 16 through insertion of the mounting legs 17 into mounting apertures of the printed circuit board 16 are formed at opposite sides of one of the legs 5 of the retainer 4, while a pair of mounting legs 18 for mounting the casing 1 on the printed circuit board 16 through insertion of the mounting legs 18 into mounting apertures of the printed circuit board 16 are formed at opposite sides of the other one of the legs 5 such that the mounting legs 17 and 18 radially confront each other.
In the casing 1, first and second rotary sliders (movable contacts) 19 and 20 made of elastic metal and a rotary member 21 made of insulating material are further provided such that the first and second rotary sliders 19 and 20 are attached to the rotary member 21. More specifically, the rotary member 21 has an operating shaft portion 24' formed at an upper portion thereof and a stopper projection 25' extending radially outwardly at a lower portion thereof and is rotatably supported by the central bore 22 of the first insulating substrate 2 and the central bore 23 of the second insulating substrate 3 such that the first and second rotary sliders 19 and 20 are, respectively, attached to upper and lower faces of the stopper projection 25', with the operating shaft portion 24' projecting out of the central bore 22 of the first insulating substrate 2. Additionally, the first rotary slider 19 has a pair of elastic contacts 24 and a pair of elastic contacts 25. The elastic contacts 24 and 25 are elastically brought into sliding contact with the first resistance element 6 and the first conductor 8 of the first insulating substrate 2 so as to short-circuit the first resistance element 6 and the first conductor 8. Likewise, the second rotary slider 20 has a pair of elastic contacts 26 and a pair of elastic contacts 27. The elastic contacts 26 and 27 are elastically brought into sliding contact with the second resistance element 7 and the second conductor 9 of the second insulating substrate 3 so as to short-circuit the second resistance element 7 and the second conductor 9. Furthermore, the casing 1 has a protrusion 26' extending radially inwardly at approximately an axial central portion thereof. It should be noted that a rotational angle of the rotary member 21 is regulated through contact of the stopper projection 25' of the rotary member 21 with the protrusion 26' of the casing 1.
Thus, in the prior art variable resistor K, since two interlocking variable resistor members are separately constituted by the first insulating substrate 2 and the first rotary slider 19 and by the second insulating substrate 3 and the second rotary slider 20, respectively and the first and second rotary sliders 19 and 20 are, respectively, attached to the upper and lower faces of the stopper projection 25' of the rotary member 21, the known variable resistor K has such an inconvenience that a difference in change of resistance value between the two interlocking variable resistor members arises due to inaccurate formation of the first and second resistance elements 6 and 7 by printing, etc. as well as by misalignment of the first and second rotary sliders 19 and 20, thereby resulting in a large interlocking error.
Furthermore, the known variable resistor K has such disadvantages that, since the number of constituent elements therefor is fundamentally equal to that of interlocking type ordinary-sized variable resistors, it is difficult to make the known variable resistor K compact in size and a number of assembly processes are required therefor, resulting in an increased production cost.
Furthermore, in the case where dip soldering is employed for soldering a rear face (provided with metal foil) of the printed circuit board 16 by inserting the terminals 10 to 15 into the mounting holes of the printed circuit board 16 and inserting the mounting legs 17 and 18 into the mounting apertures of the printed circuit board 16 as shown in FIG. 2 so as to mount the known variable resistor K on the printed circuit board 16, flux proceeding upwardly from the mounting holes and the mounting apertures of the printed circuit board 16 is likely to penetrate from contact portions between the casing 1 and the second insulating substrate 3 into the variable resistor K through the terminals 10 to 15, thereby causing improper contact. Since the second insulating substrate 3 is disposed quite adjacent to the printed circuit board 16, there is a strong possibility that flux will penetrate the casing 1 onto the second resistance element 7 and the second conductor 9. On the other hand, since the first insulating substrate 2 is rather spaced away from the printed circuit board 16, such a possibility is slim that flux will reach the first resistance element 6 and the first conductor 8. Accordingly, the prior art variable resistor K has been disadvantageous in that, since automatic soldering of the known variable resistor K to the printed circuit board 16 cannot be performed by employing dip soldering, manual soldering is required to be performed therefor, thus resulting in an increased assembly cost.
Moreover, the rotational angle of the rotary member 21 is regulated through contact of the stopper projection 25' of the rotary member 21 with the protrusion 26' of the casing 1 as described above. However, the known variable resistor K has such an inconvenience that, since the casing 1 is made of synthetic resin, etc. and the thickness of the cylindrical wall of the casing 1 cannot be made large so as to make the casing 1 compact in size, the protrusion 26' is readily deformed when subjected to even a relatively small force at the time of contact of the stopper projection 25' with the protrusion 26'.